In the case of cutting a workpiece typified by a steel plate, it is common to adopt a plasma cutting method that has a high cutting speed as compared with a gas cutting method. A plasma cutting torch is classified into a non-transfer type plasma torch and a transfer type plasma torch, and in the case of cutting a relatively thick workpiece, the transfer type plasma torch is commonly used.
In the transfer type plasma torch, a plasma gas made up of an oxygen gas or an air is supplied to a space constituted by an electrode and a nozzle, and electricity is discharged between the electrode and the nozzle to form plasma from the plasma gas so as to form a pilot ark, which is then sprayed from the nozzle, and after the pilot ark comes into contact with the workpiece, electricity is discharged between the electrode and the workpiece while the discharge between the electrode and the nozzle is stopped, to form a main arc (plasma arc), which is moved while melting part of the workpiece and also removing a melt from a base material, to perform cutting.
In the plasma cutting, part of the base material is melt by thermal energy of the plasma arc to produce a melt, and part of the base material is rapidly oxidized by action of oxygen contained in the plasma gas to produce an oxidized melt and fine particles of an oxide. The melt and the fine particles as thus produced are removed from the base material by mechanical energy of the plasma arc.
The melt of the base material and the oxidized melt drop below the workpiece and are accommodated into a slag reception bath. Further, a relatively large particle drops below the workpiece, or flies in the vicinity of the cut portion and then drops onto the top surface of the workpiece. However, there occurs a problem in that the fine particles of the oxide might fly around the workpiece to have an adverse effect upon a working environment of a factory.
For this reason, a plasma cutting device is commonly provided with a smoke ejecting device and a dust collecting device (e.g. see Patent Document 1). This technique is to form a lateral smoke path provided in juxtaposition with a partition in an orthogonal position to a rail in a space below a body of a plasma cutter, dispose a suction hood and an exhaust hood in positions corresponding to this smoke path, and connect these hoods through a duct, while providing a dust collector at the duct. Therefore, fine particles (fumes) that fly in cutting of the workpiece can be collected into the dust collector through the suction hood and the duct so as to seek improvement in operating environment of the factory.
Patent Document 1: Japanese Patent No. 1315469